ZEBRAFISH MDA5 IS ESSENTIAL FOR A VIGOROUS ANTIVIRAL RESPONSE TO RHABDOVIRUS INFECTION

ZEBRAFISH MDA5 IS ESSENTIAL FOR A VIGOROUS ANTIVIRAL RESPONSE TO RHABDOVIRUS INFECTION

By Matthew J. Pietraszewski

An Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Biochemistry)

August, 2010

Physical and mucosal barriers serve as the primary defense mechanisms for protecting against microbial infections.  Although effective, when these barriers are breached the body becomes largely dependent on the innate immune system to react to microbial invasion.  The innate immune system works on the basis of recognition of evolutionarily conserved molecules known as pathogen associated molecular patterns (PAMPs) presented as lipids, proteins, or pathogen derived RNA/DNA.  These molecules are recognized by specialized families of pattern recognition receptors (PRRs) present on most cell types.  PRRs play an indispensible role in staving off infection until appropriate adaptive immune responses can be mounted.  Recognition of various PAMPs leads to the subsequent induction of pro-inflammatory cytokines, chemokines, interferons (IFN), and co-stimulatory molecules (21).  In order to better understand how PRRs function and are manipulated by pathogens, we have chosen the zebrafish, Danio rerio, as our model organism.  The absence of a functional adaptive immune system for the first 4-6 weeks of development make the zebrafish advantageous for examining the contribution of only the innate immune response.  These data present the cloning and functional analysis of zebrafish encoded melanoma differentiation-associated gene 5 (zMDA5).  We find that zMDA5 functions as an innate PRR culminating in the activation of both IFN and nuclear factor kappa-light-chain-enhancer of activator B cells (NF-ĸB).  In addition, we find that zMDA5 participates in the recognition of Snakehead rhabdovirus which belongs to the family Rhabdoviridae.  In mammals, MDA5 has been shown to be non-essential for rhabdovirus recognition, suggesting that earlier in evolution MDA5 may have been important in the recognition of a wider array of viruses.